Project Summary

During 2021-2024, four vehicular bridges have been constructed using hybrid, fiber-reinforced polymer (FRP) composite tub (CT) girders in the United States. However, these bridges are single-span, simply supported structures, and wider application of the CT girder will require adapting it to continuous, multi-span configurations to increase design efficiency, reduce live load deflections, and improve serviceability. Indeed, two multi-span, continuous CT girder bridges are currently under construction, but their success hinges on the development of a live load continuity joint to carry negative moments at interior piers and integral abutments. While live load continuity joints are routinely used and well-understood for precast concrete girder bridge construction, their implementation in CT girder bridges is not straightforward due to the requirement that FRP bottom flange compressive stresses be transferred between discontinuous girder ends. This study directly addresses this challenge through the development of a novel CT girder live-load continuity joint that relies on a short length of concrete infill within adjacent discontinuous girders. The concrete is mechanically bonded to the purposely deformed girder interior via shear-friction, while the girder serves as concrete formwork, easing construction. A rational design methodology is presented to determine the necessary length of concrete infill given a required moment capacity and girder cross-section while also accounting for flange compressive buckling. A heavily instrumented, large-scale prototype is tested to failure to assess joint performance, and measured strains are compared with calculated values. The efficiency gains made possible by the live load continuity joint are then assessed via a realistic design scenario. The joint exhibited 11.4% more moment capacity than predicted based on the expected failure stress at the FRP-concrete shear-friction interface. The design example showed that live load continuity results in a significant reduction in girder depth and the amount of carbon fiber needed in the girder compression flange.